Justification:
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

The global population is estimated to number > c.300,000 individuals (Wetlands International 2006), while national population sizes have been estimated at c.50-10,000 wintering individuals in China and c.100-10,000 breeding pairs in Russia (Brazil 2009).

Behaviour This species is fully migratory and travels on a narrow front via specific routes using well-known stop-over sites (Madge and Burn 1988) between its Arctic breeding and temperate wintering grounds (del Hoyo et al. 1992). It arrives on the breeding grounds from early-May to late-June (Madge and Burn 1988) (depending on local conditions [Kear 2005a]) where it breeds well-dispersed (Snow and Perrins 1998) in single pairs (del Hoyo et al. 1992), occasionally nesting semi-colonially in optimum habitats (Madge and Burn 1988, Kear 2005a). After breeding the species undergoes a flightless moulting period lasting for c.30 days between late-June and early-September, gathering in flocks on open waters (Madge and Burn 1988, Scott and Rose 1996). Family groups leave the breeding grounds from early-September to late-October (Madge and Burn 1988) and arrive on the wintering grounds from mid-October onwards (Madge and Burn 1988). During this autumn migration some groups may remain at stop-over sites until moved on by cold weather (Madge and Burn 1988). The return northward migration occurs from early-March, with the species travelling in small parties that disperse on arrival in the Arctic (Madge and Burn 1988). The species is gregarious outside of the breeding season, often gathering into large flocks of hundreds or thousands of individuals on the wintering grounds (Madge and Burn 1988, Kear 2005a). The species forages by day (where undisturbed [del Hoyo et al. 1992]) and roosts at night on open water (Kear 2005a). Habitat Breeding The species breeds near shallow pools, lakes (del Hoyo et al. 1992) and broad slow-flowing rivers (del Hoyo et al. 1992, Kear 2005a) with emergent littoral vegetation and pondweeds (e.g. Potamogeton spp.) connected to coastal delta areas (Kear 2005a) in open, moist, low-lying sedge-grass or moss-lichen (Kear 2005a) Arctic tundra (del Hoyo et al. 1992). It rarely nests in shrub tundra, and generally avoids forested areas (Kear 2005a). Non-breeding On migration the species frequents shallow ponds (Kear 2005a), lowland and upland lakes (Madge and Burn 1988, Kear 2005a), reservoirs (Madge and Burn 1988), riverine marshes, shallow saline lagoons (Kear 2005a) and sheltered coastal bays and estuaries (Madge and Burn 1988). During the winter it inhabits brackish and freshwater marshes (Madge and Burn 1988), rivers, lakes, ponds (Kear 2005a) and shallow tidal estuarine areas (del Hoyo et al. 1992, Kear 2005a) with adjacent grasslands (del Hoyo et al. 1992), flooded pastures (Kear 2005a) or agricultural arable fields (del Hoyo et al. 1992, Kear 2005a) below 100 m (Snow and Perrins 1998). Diet The species is predominantly herbivorous (del Hoyo et al. 1992), its diet consisting of the seeds, fruits, leaves, roots, rhizomes and stems of aquatic plants (e.g. Potamogeton, Zostera and Glyceria spp.), grasses (del Hoyo et al. 1992), sedges, reeds (Phragmites and Typha spp. [Kear 2005a]) and herbaceous tundra vegetation (Kear 2005a). During the winter the species complements its diet with agricultural grain and vegetables (del Hoyo et al. 1992) (e.g. potatoes [del Hoyo et al. 1992] and sugar beet [Kear 2005a]), and may also take estuarine invertebrates such as molluscs, amphipods (e.g. Corophium spp.) and polycheate worms on tidal mudflats prior to migration (Kear 2005a). Breeding site The nest is a large mound of plant matter positioned on elevated ground (del Hoyo et al. 1992) such as a ridge or hummock, often at some distance from feeding poolsto reduce to the risk of flooding (Kear 2005a). The species may re-use a nest from the previous year or build a new one, and although it is not colonial, many pairs may nest close together in optimum habitats (e.g. 5-16 pairs per 10 km2 [Kear 2005a]). Management information An experiment carried out in the Sacramento National Wildlife Refuge, California found that in wetland habitats where clay hardpans underlie wetland sediments tilling (plowing) the soil may be an effective means of reducing lead shot availability to waterfowl (Thomas et al. 2001). Plowing was found to reduce the amount of shot available to depths of 20-30 cm (below the foraging zone of the species [Thomas et al. 2001]).

The species is threatened by the degradation and loss of wetland habitats due to drainage (Kear 2005a) (e.g. for agriculture [Grishanov 2006]), petroleum pollution, peat-extraction, changing wetland management practices (e.g. decreased grazing and mowing in meadows leading to scrub over-growth), the burning and mowing of reeds (Grishanov 2006) and eutrophication (Kear 2005a). Its Arctic breeding habitat is also threatened by oil and gas exploration (Kear 2005a). The species is threatened by mortality from oil pollution (oil spills) in moulting and pre-migrational staging areas, from collisions with powerlines, and from lead poisoning as a result of lead shot (del Hoyo et al. 1992, Kear 2005a) and fishing weight ingestion during migration and on wintering grounds (Kear 2005a). The species suffers from poaching in north-west Europe, is hunted for sport in North America (del Hoyo et al. 1992, Kear 2005a) and is hunted considerably for subsistence throughout its range (del Hoyo et al. 1992). The species is also susceptible to avian influenza, so may be threatened by future outbreaks of the disease (Melville and Shortridge 2006).

Citation:

BirdLife International 2012. Cygnus columbianus. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 03 March 2015.